Exceptional n-Type Thermoelectric Performance in Anisotropic K ₂ Te ₃ via Lone-Pair Electron and Dual-Rattling Mode Engineering

This study systematically reveals the bonding characteristics, anisotropic phonon transport, and electronic structure of K 2 Te 3, along with their regulatory mechanisms on thermoelectric performance based on first-principles calculations. The analysis shows that the stereochemically active lone-pair electrons of Te induce local structural distortion, which enhances lattice anharmonicity; the dual-rattling-like vibrational modes (independent vibrations of Te clusters and K atoms) further strengthen phonon scattering. Band anisotropy enables spatial decoupling of the Seebeck coefficient and electrical conductivity: the a -axis direction exhibits high electrical conductivity, while the flat band along the b -axis contributes to a high Seebeck coefficient. Consequently, the a -axis achieves both a high zT value (2.73 at 700 K) and an ultralow thermal conductivity (0.41 W/mK at 300 K). Ultimately, n -type K 2 Te 3 demonstrates excellent thermoelectric performance along the a -axis, highlighting the critical role of anisotropic design in enhancing thermoelectric material properties.